In automotive refinish, major damage sites are typically treated by removing the damaged parts of the bodywork and refinishing their entire area. In instances of minor damage, which are very annoying particularly in the case of new and/or particularly high-value vehicles, damage of a kind such as key scratches or knocks (for example, from the demarcation in a parking lot), for instance, this procedure is very involved and is out of proportion with the extent of the damage. Minor damage is therefore removed preferably with the aid of methods of minor vehicle refinish. These methods are also referred to by those in the art as touch-up or spot repair.
The known spot repair methods, however, have numerous disadvantages and are difficult to implement. For instance, the runout zones of the clearcoat spray mist on the original finish are often too wide, which makes it more difficult to achieve a visual match between refinish and original finish. Additionally, because of the poor adhesion of the original finish in the runout zones around the damage site, the refinish clearcoat may break away or come off. That produces clearly visible edges which may even run all the way round the refinish clearcoat, which is located directly above the original finish. In that case the overall effect of the refinish, owing to the visually harsh transition zones, is that of a “sticking plaster”.
Attempts have been made to solve the problems of the breaking away or coming off and the difficulty of matching the visual qualities in the runout zones by applying what are called spot blenders over the uncured refinish clearcoat. The purpose of this measure is to produce particularly “gentle” transition zones and to prevent the refinish clearcoat coming away in the zones marginal to the original finish.
German patent application DE 100 43 810 A1 discloses a spot repair method with which the sanding and/or polishing times can be lowered by more than 50% as compared with conventional methods. The spot repair binder composition known from DE 100 43 810 A1, however, is suitable only for two-component clearcoat materials based on hydroxyl-containing binders. Other clearcoats, especially one-component clearcoats, cannot be produced by means of the spot repair method of DE 100 43 810 A1.
The German patent application DE 10 2005 012 589 A1, entitled “UV-A-curable, solvent-containing mixture, process for preparing it, and use thereof” discloses a composition consisting of the following constituents:    (A) 1% to 50% by weight of at least one UV-A-curable constituent selected from the group consisting of monomers (a1)) containing at least three UV-A-curable reactive functional groups and at least one isocyanate-reactive functional group and mixtures (a2) of monomers (a21) that are free from isocyanate-reactive functional groups and contain at least two UV-A-curable reactive functional groups, and monomers (a22) that contain at least two UV-A-curable reactive functional groups and at least one isocyanate-reactive functional group;    (B) 0.01% to 10% by weight of at least one colorless or substantially colorless photoinitiator having at least one absorption maximum in the wavelength range of λ=300 to 400 nm;    (C) 10% to 70% by weight of at least one alkyl and/or cycloalkyl acetate having 3 to 10 carbon atoms in the alkyl radical and/or in the cycloalkyl radical;    (D) 10% to 70% by weight of at least one alkoxyalkyl, alkoxycycloalkyl, cycloalkoxyalkyl and/or cycloalkoxycycloalkyl acetate;    (E) 0.001% to 5% by weight of at least one constituent that lowers the interfacial tension; and    (F) 0% to 50% by weight of at least one alkylaromatic having at least two alkyl radicals having 1 to 6 carbon atoms in the molecule; and    (G) 0% to 50% by weight of at least one additive different from constituents (A) to (F).
A disadvantage of this composition is that, like the composition known from DE 100 43 810 A1, it lacks simultaneous universal suitability for one- and two-component clearcoat materials and, furthermore, after curing under UV irradiation, always still produces slight marginal marks at the polishing edge.
It is an object of the present invention, accordingly, to provide a curable composition to which can be used as a spot blender in spot repair methods and which can be used in combination with one-component and two-component clearcoat materials, preferably without alteration to the constitution of the curable composition. The curable compositions ought preferably to be curable both with UV radiation and thermally, and also by thermal means alone.
The composition to be provided in accordance with the invention ought further, preferably, to make it possible to produce refinishes which within a very short time can be sanded and/or polished, which no longer stand out visually from the original finish, which no longer exhibit any breaking away or coming off in the runout zones, and which are of such high quality that they can also be used for automotive spot repair of original finishes on the production line.
This object is achieved by means of a binder-free spot blender composition for one- and two-component clearcoat materials.